Clinton highlighted Trump "bizarrely" praising Putin. At the NBC News Forum, Trump touted the Russian leader's "82 percent approval rating," predicted he would have a "very very good relationship" with Putin, and compared Putin favorably to Obama.

"That is not just unpatriotic and insulting to the people of our country," Clinton said, "it is scary because it suggests he will let Putin do whatever Putin wants to do."

The Democratic nominee took six questions during her podium press conference.

Clinton clarified a remark from Wednesday's Forum—where she said that if elected "we are not putting ground troops into Iraq ever again"—stating Thursday that she does support the air campaign and special forces.

She added: "I will absolutely be prepared to do whatever is necessary to support the Arab and Kurdish fighters on the ground to take out as much of the infrastructure of ISIS from the air to go after Baghdadi with a very focused commitment to taking him off the battlefield."

Responding to questions from the tarmac, Clinton reacted to criticism that she didn't smile enough at the Forum—saying she was "talking about serious issues"—and also took a swipe at Gov. Gary Johnson, who earlier Thursday morning earnestly asked what Aleppo is.

Clinton said she will be convening a bipartisan meeting on national security on Friday, focused on defeating ISIS.

"We should make it a top priority to hunt down the leader of ISIS," she said, adding, "I believe it will send a resounding message that no one directs or inspires attacks against the U.S. and gets away with it."